This application claims the priority of Korean Patent Application No. 2001-79723, filed Dec. 15, 2001, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a micromirror actuator and a manufacturing method thereof, and more particularly, to an actuator which can actively be driven so as to precisely control driving angle of a micromirror, and a manufacturing method thereof.
2. Description of the Related Art
In general, optical switches select an optical path to allow an optical signal to be transmitted from a predetermined input port to a predetermined output port. Referring to FIG. 1, a plurality of micromirror actuators 10 are arranged in the form of two-dimensional matrix. Light beams emitted from optical fibers 43 of an input portion are changed to collimated light beams via micro lenses 45. The collimated light beams are incident and reflected on corresponding micromirrors 31a-31d that stand erect, and then transmitted to optical fibers 48 of an output portion via micro lenses 46. In other words, an optical switch selects optical paths so that incident optical signals are reflected on micromirrors 31a, 31b, 31c, and 31d that stand erect over a substrate 15 while they pass over micromirrors 32 that are parallel with the surface of the substrate 15. For example, a micromirror 31a in the fourth row of the first column, a micromirror 31b in the third row of the second column, a micromirror 31c in the first row of the third column, and a micromirror in the second row of the fourth column stand erect to be perpendicular to the substrate 15, and the other micromirrors are parallel with the surface of the substrate 15 so that the optical signals are transmitted to desired optical paths.
FIG. 2 shows a conventional micromirror actuator 10 using an electrostatic force. A trench 5 is formed in a substrate 15. Supporting posts 20 stand erect beside both sidewalls of the trench 5. The supporting posts 20 support torsion bars 25 with which a micromirror 30 is joined to be capable of rotating. The micromirror 30 is composed of an actuator 30a that faces the trench 5 using the torsion bars 25 as shafts when the micromirror 30 is parallel with the surface of the substrate 15, and a reflector 30b. 
FIG. 3 is a cross-sectional view taken along ling II—II of FIG. 2. A lower electrode 37 is formed at the bottom of the trench 5, and a side electrode 40 is formed on one sidewall of the trench 5 so as to drive the micromirror 30 by electrostatic forces generated through interaction with the actuator 30a. In other words, an electrostatic force operates between the lower electrode 37 and the actuator 30a so that the micromirror 30 rotates downward. After the micromirror 30 rotates to some extent, an electrostatic force operates between the actuator 30a and the side electrode 40 so that the micromirror 30 sequentially rotates and stands erect. The micromirror 30 is elastically supported by the torsion bars 25 to be capable of rotating. After the electrostatic forces are released, the micromirror 30 is restored to its parallel state by a restoring force of the torsion bars 25.
The side electrode 40 generates an electrostatic force through an electrical interaction with the micromirror 30 and serves as a stopper that supports the micromirror 30 so as to maintain its accurate right angle when standing erect. For the side electrode 40 serving as the stopper, the torsion bars 25, which are a rotation shaft of the micromirror 30, have to be correspondingly positioned on a plane which extends to include the side electrode 40. In a case where the torsion bars 25 are positioned outside the plane including the side electrode 40, the micromirror 30 cannot stand erect. FIG. 4A shows the torsion bars 25 that are positioned outside the sidewall of the trench 5 where a driving angle θ1 of the micromirror 30 is smaller than 90°. FIG. 4B shows the torsion bars 25 that are positioned inside the sidewall of the trench 5 where a driving angle θ2 of the micromirror 30 is greater than 90°.
The torsion bars 25 and the sidewall of the trench 5 have to be positioned accurately on the same level so that the micromirror 30 stands erect at an angle of 90°. However, a relative position difference between the torsion bars 25 and the sidewall of the trench 25 due to manufacturing tolerance of an actuator of the micromirror 30, differences in a right-angle degree of the sidewall of the trench 5 and planarity of the micromirror 30, and the like causes inevitable deviation. Although an error in such a manufacturing process is slight, the error affects insertion loss that is a very important element in an actuator for an optical switch. Accordingly, after the manufacture of the micromirror actuator is completed, it is required to correct a relative position difference between the torsion bars and the sidewall of the trench occurring due to the error of the manufacturing process.